upgrading server software

hey folks got a simple (?) question to ask.. tinkering around with a g2 server that has nt enterprise on it. i am figuring that nt is outdated i have bought a upgrade of win 2000 server that only has 5 cals. do the 25 cals from nt transfer?just wonderingoh another thing is it worth puttin a copy of windows on the server besides the server software like xp home or pro? i am jsut using it as terminal servertom